Gas sensors are known for measuring a gas component in a gas mixture using semiconductor means. These gas sensors measure the gas concentration by changes which occur in the surface conductivity thereof; this is caused by adsorption on the semiconductor surface of the gas component that is to be measured. To increase the sensitivity of the semiconductor sensors, metallic admixtures are for instance added to the sensors. Specific admixtures of metallic substances produce a specific sensitivity of the semiconductor sensor to a gas component that is to be measured. However, if this gas component that is to be measured does not occur for a relatively long period in the gas mixture in which the semiconductor is located, then the semiconductor loses its sensitivity. To overcome this, the semiconductor sensor is for instance exposed briefly to a small quantity of the gas component that is to be measured, which causes its sensitivity to increase once again.
If a fresh, still unused semiconductor sensor is repeatedly exposed during its period of operation to the gas component that is to be measured, its sensitivity can initially decrease before it attains a stable final value. The semiconductor sensor ages. Such aging can be performed artificially with fresh semiconductor sensors before they are installed at the location where they will be used for measurement.
A method for stabilizing semiconductor gas sensors of the type referred to above is disclosed in German published patent application DE-OS No. 31 16 244. In the known method, the semiconductor gas sensor is introduced once into a gas atmosphere that contains the gas component that is to be measured at the location where the semiconductor gas sensor is later installed.
This type of aging method requires only that the semiconductor gas sensor, before it is installed, be exposed to the gas component that is to be measured and which is at a more or less high gas concentration. The aging of a semiconductor sensor is a long-term process, however, and it is not completed after a single performance of the known method. Furthermore, a relatively long period may elapse, even for an aged sensor, between its installation and the first time that the presence of the gas component that is to be measured occurs. In the meantime, the sensor continues to lose sensitivity because it has not been exposed to the gas component that is to be measured for a relatively long period. Even a semiconductor sensor that is already installed at the location where measurement will be performed would have to be exposed repeatedly to the gas component that is to be measured, if there are long intervals between measurements. However, a method of this type would require a substantial effort, because a semiconductor gas sensor that has already been installed would have to be exposed periodically, via a calibrating device disposed elsewhere than at the measurement location, to a predetermined gas concentration of the gas component that is to be measured.